STORY: The International Atomic Energy Agency is drawing up a report after its inspectors crossed the front line last week to reach the imperiled facility that Ukraine and Russia have accused each other of shelling, risking a nuclear disaster.

Two IAEA experts are now set to stay on indefinitely at the facility in southern Ukraine - Europe's largest nuclear plant - which was captured by Russian troops at the beginning of March shortly after their invasion.

Petro Kotin, head of Ukraine's state nuclear company Energoatom, told Reuters that the establishment of a permanent mission was a "good" step but that the "root of the problem" remained as Russian troops controlled the site.

"We need results from this mission actually. These results should (resolve) the whole situation: de-occupation. If not, then we must have some kind of viable results," he said.